Foam insulated prestressed concrete wall



Oct. 8, 1963 Frx. CROWLEY FOAM INSULATED PRESTRESSED CONCRETE WALL FiledJune 20, 1962 I N VEN TOR. BY w" WW9 CONTINUOUS STEEL DIAPHRAGMPOLYSTYRENE FOAM Uni ed States Patent FOAM INSULATED PRESTRESSEDCONCRETEYWALL Francis X. Crowley, Broolrline, Mass, assignor toCllriowley Hessian Engineers, Boston, Mass, a partner- S P Filed June20, 1962, Ser. No. 206,120 1 2 Claims. (Cl. 138-476) This inventioncomprises a new and improved wall structure for tanks and the like thatin use must efficiently protect their contents against loss of heat. Thestructure of my invention is characterized by the encasement inprestressed concrete of sheets or slabs of heat-insulating material thatis elastomeric to the extent that it is capable of absorbing oradjusting itself to changes in operating pressures and temperaturewithout in any way impairing the integrity of the wall structure ofwhich it is a component.

One important field of use for my invention is in the construction ofdigester tanks for sewage in which the contents must be maintainedcontinuously at an elevated temperature to insure the requiredbacteriological reaction, i.e. at 90 to 100 F. for optimum conditions.Herctofore such tanks have been built at very considerable expense toinclude an inner concrete wall and an outer brick wall spaced therefromby an annular dead air space or a space packed with heat insulatingmaterial.

The structure of my invention is not only much less expensive to buildboth from the standpoint of labor and materials but has 50100% greaterheat insulating efficiency.

These important advantages may be achieved in a structure selected as apreferred embodiment of my invent-ion and shown in the accompanyingdnawing, in which:

FIG. 1 is a view in longitudinal or vertical section, and

FIG. 2 is a fragmentary view in horizontal cross section.

The first step in constructing a tank such as that shown in FIGS. 1 and2 is to erect a diaphragm of sheet metal in the form of an uprightcylindrical enclosure of the desired diameter, for example 20-40 feet.The diaphragm as herein shown is formed with vertically disposedcorrugations. 'Layers of concrete are next applied to the inner concaveface of the diaphragm 10 and to its outer convex face. These layers ofconcrete are applied by the well known Gunite process in accordance withwhich a mixture of sand and cement in water is blasted under airpressure against the supporting surface. In this manner an inner layer11 and an outer layer 12 are formed which are coextensive in area withthe metal diaphragm and present substantially smooth and continuouslycylindrical surfaces.

To the outer convex surface of the concrete layer 12 are now afiixedrectangular slabs 13 of a sponge heatinsulating sheet material, such aspolystyrene or polyurethane foam. These slabs as shown in FIG. 2 arespaced slightly from each other in :a circumferential direction and maybe 2' x 8' in area and 2" or 3" in thickness. They maybe initiallysecured in place by adhesive cement or any other convenient means.Having distributed and assembled heat-insulating slabs as suggested inFIG. 2, the assembled components are encased in an outer wall ofconcrete 14 which bonds itself to the convex wall 12 in the spaced areas15 between the longitudinal sides of the slabs 13 as well as above andbelow the slabs so that the latter are completely concealed and encased.Preferably, the outer layer 14 is applied by the same Gunite process asbefore and this layer may be provided with wire mesh reinforcing 16.

Paten te-d Oct. 8, 1963 "ice wrapped with wire or wire bands 17 and.these' are s-ub-' jected to severe tension in order to hold thestructure under prestressed compression. A suitable wire for thispurpose is cold-drawn high carbon steel wire 0.162 in diameter having anultimate strength of 210,000 p.s.i. and a work stress of 105,000 p.s.i.

Having placed the wire 17 under the required tension, a final outercover-coat 18 of concrete is applied to the circumferential surface ofthe tank concealing and encasing the wire bands 17 and imparting asmooth surface finish to the tank. This coating is also preferablyapplied by the Gun-ite process. The whole structure as herein shown iserected upon a solid concrete base 19 which may be shaped to provide aconcave bottom for the tank and a flat annular flange to which the wallstructure is connected by any conventional form of leakproof joint assuggested in FIG. 1. Also as herein shown the upper rim of the wallstructure may be thickened for ornamental or structural reasons and acircumferential flange 20 may be molded at any desired level as .a partof the inner concrete layer 11. This may be secured in place by anchorbolts afiixed in spaced relation to the metal diaphragm 10, and may beemployed to support a cover or staging inside the tank.

Comperative figures emphasize insulating efficiency of the novel wallstructure above described, in each case the outer surface beingsubjected to wind 15 mph. and the tank containing warm sludge in contactwith its inner surface now as follows:

7 U 8" concrete wall-- 1.2. 4" brick+2 Air-H2" concrete 0.36 4" brick+2airspace+-8" concrete 0.41 2 /2 Gunite+2 polystyrene-H Gunite 0.20

Where U values indicate the amount of heat loss through the walls of thedifferent types listed. From this it will be seen that a tank of myimproved structure is more than twice as effective against heat loss asthe more conventional tank having walls of 4" brick+2" airspace+8concrete.

While I prefer to employ polystyrene sponge as the material of the slabs13'any equivalent elastomeric foam or sponge may be substituted withinthe scope of the invention.

The composite wall, comprising the inner concave layer 11, the metaldiaphragm 10 and the convex layer 12, may be termed the core wall andmay be varied in the shape and character of its components. In a broadaspect the invention may be defined as a process characterized by thesteps of constructing a core wall, encasing elastomeric sponge thereonwithin a covering layer and subjecting the whole structure to permanentprestress applied outside the encased elastomeric sponge.

This application is a continuation in part of allowed application SerialNo. 838,733, [filed September 8, 1959, now abandoned.

Having thus disclosed my invention and described in detail a preferredembodiment thereof, I claim as new and desire to secure by LettersPatent:

1. A heat insulating wall for digester tanks and the like, comprising acontinuous metal diaphragm in the form of an upright cylindricalenclosure having vertical stiffening corrugations on its surface,concave and convex walls of concrete enclosing the corrugated metaldiaphragm between them and presenting substantially smooth andcontinuous cylindrical surfaces, separate rectangular slabs ofheat-insulating elastomeric foam conformed to the outer cylindricalsurface of the convex concrete wall and affixed thereto incircumferential spaced relation, an outer concrete wall encasing saidelastomeric slabs and being bonded to the convex concrete wall in thespaced areas between the slabs, pre tensioned wire wrapped in continuouscircular bands about the outer concrete wall so as to hold undercompression the entire wall structure including the elastomeric slabs,and a cover layer of concrete encasing said wires.

2. A heat-insulating Wall for digester tanks as above described, furthercharacterized in that the said el-astomeric slabs are of polystyrenefoam.

References Cited in the file of this patent UNITED STATES PATENTS2,326,010 Crorn Aug. 3, 1943 2,777,295 Bliss et a1 a Jan. 15, 19572,849,028 Clark et a1 r Aug. 26, 1958 2,888,819 Sitton June 2, 19592,933,917 Sampson Apr. 26, 1960 2,964,821 Meehan Dec. 20, 1960 OTHERREFERENCES Styrofoam, Technical Data, published by Dow Chemical Co.,1947. (Copy in file in Division 15), Class 18/488.

1. A HEAT INSULATING WALL FOR DIGESTER TANKS AND THE LIKE, COMPRISING ACONTINUOUS METAL DIAPHRAGM IN THE FORM OF AN UPRIGHT-CYLINDRICALENCLOSURE HAVING VERTICAL STIFFENING CORRUGATIONS ON ITS SURFACE,CONCAVE AND CONVEX WALLS OF CONCRETE ENCLOSING THE CORRUGATED METALDIAPHRAGM BETWEEN THEM AND PRESENTING SUBSTANTIALLY SMOOTH ANDCONTINUOUS CYLINDRICAL SURFACES, SEPARATE RECTANGULAR SLABS OFHEAT-INSULATING ELASTOMERIC FOAM CONFORMED TO THE OUTER CYLINDRICALSURFACE OF THE CONVEX CONCRETE WALL AND AFFIXED THERETO INCIRCUMFERENTIAL SPACED RELATION, AN OUTER CONCRETE WALL ENCASING SAIDELASTOMERIC SLABS AND BEING BONDED TO THE CONVEX CONCRETE WALL IN THESPACED AREAS BETWEEN THE SLABS, PRE-TENSIONED WIRE WRAPPED IN CONTINUOUSCIRCULAR BAND ABOUT THE OUTER CONCRETE WALL SO AS TO HOLD UNDERCOMPRESSION THE ENTIRE WALL STRUCTURE INCLUDING THE ELASTOMERIC SLABS,AND A COVER LAYER OF CONCRETE ENCASING SAID WIRES.